The majority of fastener driving tools in use today are pneumatically actuated tools. Pneumatic fastener driving tools have been developed to a high degree of sophistication and efficiency, but require a source of air under pressure and are literally tied thereto by hose means. Under some circumstances, particularly in the field, a source of air under pressure is not normally present and is expensive and sometimes difficult to provide.
Prior art workers have also developed a number of electro-mechanical fastener driving tools, usually incorporating one or more flywheels with one or more electric motors therefor. Such tools require a source of electrical current which is normally present at the job site. However, this type of tool is also quite literally "tied" to a power source.
Under certain circumstances, it is desirable to utilize a completely self-contained fastener driving tool, not requiring attachment to a source of air under pressure or a source of electrical current. To this end, prior art workers have devised self-contained fastener driving tools powered by internal combustion of a gaseous fuel-air mixture. It is to this type of tool that the present invention is directed.
Exemplary prior art internal combustion fastener driving tools are taught, for example, in U.S. Pat. Nos. 2,898,893; 3,042,008; 3,213,607; 3,850,359; 4,075,850; 4,200,213; 4,218,888; 4,403,722; 4,415,110; and European Patent Applications Nos. 0 056 989; and 0 056 990. While such tools function well, they are usually large, complex, heavy and awkward to use.
The fastener driving tool of the present invention comprises a self-contained internal combustion tool which is compact, easy to manipulate and unusually simple in construction. The fastener driving tool is highly efficient, operating on a moderate compression ratio to convert most of the fuel energy into useful work. The tool carries a replaceable canister of gaseous fuel and a replaceable canister of oxidizer. This eliminates the necessity for a combustion air chamber and its attendant passages and valving, as well as a second cylinder and piston acting as a compressor during the tool cycle to replenish air under pressure in a combustion air chamber. As a result, the tool has a single cylinder, provided with a piston/driver which, during a tool cycle, drives a fastener into a workpiece and fills a return air chamber (to which the cylinder is connected) with air under pressure.
The fastener driving tool is provided with a positive, trigger-actuated cam system which sequences the tool through its cycle, upon actuation of the trigger. The cam system operates a series of two-way valves and an ignition device.